On the other side of the galaxy a mining company is exploiting the already unstable planet of Syra for every precious mineral it contains. River Song is attempting to save the native people. She needs the Doctor's help, but she also knows he mustn't yet discover her true identity. The final confrontation sees the Doctor once again face his enemy the Eleven in an attempt to prevent the destruction of Syra and the genocide of its inhabitants.
River shows Helen three pictures of the Doctor in her diary to find out which incarnation she is traveling with: the magicial, the spiff, or the geography teacher, but Helen says she is not travelling with any of them, then points out the Eighth Doctor's image and says she is travelling with him. River realises she cannot meet the Eighth Doctor or it will interfere with their timelines. (TV: The Time of Angels, The Husbands of River Song)